Documents 1 to 5 all disclose an apparatus which detects a fuel pressure supplied to an injector by a fuel pressure sensor and detects a fuel pressure waveform that is pressure change caused by fuel injection. The apparatus calculates injection condition based on the fuel pressure waveform. For example, since the fuel pressure waveform begins dropping in response to an initiation of injection, it is possible to calculate an injection start timing by detecting a start timing of the pressure dropping. According to the apparatus, it is possible to control injection condition to a desired condition by carrying out a feedback control on operation of an injector based on the calculated injection condition.
A body of the injectors disclosed in the documents 1 to 5 is formed with a supply inlet, a nozzle hole, and passages. The supply inlet receives fuel delivered from a common rail, which is also known as a pressure accumulation container. The nozzle hole is provided to inject fuel. The passages include a main passage extending from the supply inlet to the nozzle hole and a branch passage which is branched from the main passage. The documents 1 to 5 also disclose a fuel pressure sensor disposed to detect a pressure of fuel in the branch passage. According to the structure, fuel pressure in the main passage first drops at a portion close to the nozzle hole in response to a beginning of injection from the nozzle hole. Then, pressure change travels through the main passage and the branch passage, and then, reaches to the fuel pressure sensor. Therefore, the fuel pressure sensor detects the traveled pressure change as a fuel pressure waveform.
However, a traveling speed of pressure in the main passage and the branch passage varies as a temperature of fuel is changed. As a result, a correlation between the fuel pressure waveform and the injection condition is also varied as a temperature of fuel is changed. For example, a delay time from a beginning of injection to the pressure dropping timing is varied as a temperature of fuel is changed.
In order to reduce influences caused by a fuel temperature, the apparatuses in the documents 1 to 5 has sensors for detecting fuel temperature in the branch passage. The apparatuses tried to calculate the injection condition in an accurate manner by correcting the fuel pressure waveform based injection condition calculating processing based on a fuel temperature detected by the fuel temperature sensor.
Document 1: JP-2010-285887A
Document 2: JP-2010-285889A
Document 3: JP-2010-286280A
Document 4: JP-20114842A
Document 5: JP-2011-1915A